Spinel-type lithium-manganese oxide containing heteroelements, preparation process and use thereof

ABSTRACT

A high-performance spinel-type lithium-manganese oxide for use as a material for a positive electrode of a Li secondary battery with inhibited Mn dissolution in an organic electrolyte, which is represented by the following formula: 
     
       
         {Li}[Li x .M y .Mn (2−x−y) ]O 4+d   
       
     
     wherein { } represents the oxygen tetrahedral sites in the spinel structure and [ ] represents the oxygen octahedral sites in the spinel structure, 0&lt;x≦0.33, 0&lt;y≦1.0, −0.5&lt;d&lt;0.8, and M represents at least one heteroelement other than Li and Mn, is disclosed.

BACKGROUND OF THE INVENTION

The present invention relates to a spinel-type lithium-manganese oxidecontaining at least one heteroelement (M) other than Li and Mn, as wellas a preparation process and the use thereof.

Manganese oxides have been used for many years as an active material inelectric cells. In recent years, lithium-manganese oxides which arecomposite materials of manganese and lithium as well aslithium-manganese oxides in which manganese in said lithium-manganeseoxides is partially replaced by at least one heteroelement haveattracted attention for use as an active material for positiveelectrodes of lithium secondary batteries which are capable of providinghigh output and high energy density.

Composite oxides of Li and various metals such as Co, Ni, Mn have beenproposed as a material for positive electrode of lithium secondarybatteries, which are required to have a high voltage working range, ahigh discharge capacity and a high cycle stability of charge anddischarge.

A spinel-type LiMn₂O₄, which is one type of a composite oxide of Li andMn, has been known to show a two-stage discharge, the first dischargestage being at a level of near 4V and the second discharge stage beingat a level of near 3V. It seems to be promising as an active materialfor a positive electrode because it would be expected to provide highenergy output if it could be reversibly cycled in a working range around4V.

However, it has recently been found that Mn in the LiMn₂0₄ structuredissolves in organic electrolytes when charge and discharge is conductedusing LiMn₂O₄ as an active material for lithium secondary batteries.Furthermore, our experiments revealed that as much as 1 mol % of the Mncontent in the structure may dissolve when LiMn₂O₄ is merely stored at85° C. in some organic electrolytes without performing charge anddischarge, and that characteristics as an active material for a positiveelectrode significantly deteriorate after dissolution.

This means that Mn in the LiMn₂O₄ structure used as a positive electrodefor lithium secondary batteries may dissolve in organic electrolytesafter long-term storage without performing charge and discharge, therebycausing a failure of the positive electrode in lithium secondarybatteries.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a high-performancespinel-type lithium-manganese oxide for use as a material for positiveelectrodes of a Li secondary battery with inhibited Mn dissolution in anorganic electrolyte, as well as a high-performance lithium secondarybattery using said lithium-manganese oxide as a positive electrode.

As a result of careful investigation, it has been found that the aboveobject can be achieved by using a spinel-type lithium-manganese oxidecontaining at least one heteroelement (M) other than Li and Mn whereinMn is replaced by Li and M, represented by the following formula:

{Li}[Li_(x).M_(y).Mn_((2−x−y))]O_(4+d)

wherein { } represents the oxygen tetrahedral sites (8a sites) in thespinel structure and [ ] represents the oxygen octahedral sites (16dsites) in the spinel structure, 0<x≦0.33, 0<y≦1.0, −0.5<d<0.8, with saidd value being negative when the calcination atmosphere is a reducingatmosphere, and being positive when it is an oxidizing atmosphere, and Mrepresents at least one heteroelement other than Li and Mn.

Further, we found a process for preparing the spinel-typelithium-manganese oxide containing at least one heteroelement (M) otherthan Li and Mn according to the present invention as well as ahigh-performance lithium secondary battery using the spinel-typelithium-manganese oxide containing at least one heteroelement (M) otherthan Li and Mn according to the present invention as an active materialfor a positive electrode, and thus accomplished the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying FIG. 1 shows a schematic, sectional view of a batteryassembly in which a spinel-type lithium-manganese oxide according to thepresent invention is employed as an active material for a positiveelectrode.

The accompanying FIG. 2 shows a microphotograph showing the structure ofthe particles of the spinel-type lithium-manganese oxide obtained inExample 3, and the accompanying FIG. 3 shows a microphotograph showingthe structure of the particles of the spinel-type lithium-manganeseoxide obtained in Example 6.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will now be specifically explained.

The spinel-type lithium-manganese oxide containing at least oneheteroelement (M) other than Li and Mn according to the presentinvention has the following formula:

{Li}[Li_(x).M_(y).Mn_((2−x−y))]O_(4+d)

wherein { } represents the oxygen tetrahedral sites in the spinelstructure and [ ] represents the oxygen octahedral sites in the spinelstructure, 0<x≦0.33, 0<y≦1.0, −0.5<d<0.8, and M represents at least oneheteroelement other than Li and Mn.

Preferably, said element M exists at the oxygen octahedral sites in thespinel structure to form a spinel-type lithium-manganese oxide with acubic crystal spinel structure having a lattice constant (a) of not lessthan 8.19 angstroms and not more than 8.24 angstroms.

Non-cubic spinel structures such as tetragonal crystals are notpreferable because working potential is lower with the result that theavailable energy is reduced when they are used to construct a Lisecondary battery.

Lattice constants (a) outside said range are not preferable becausemanganese in the structure becomes unstable thereby causing increased Mndissolution.

Said element M is at least one element selected from the groupconsisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ti. Zr, V, Nb, Ta, Cr, Mo, W,Fe, Co, Ni, Cu, Ag, Zn, B, Al, Ga, In, Si, Ge, Sn, Pb, P, As, Sb and Bi.

Preferably, the spinel-type lithium-manganese oxide containing at leastone heteroelement according to the present invention has an averagediameter of aggregated particles of 1-50 μm and a BET specific surfacearea of 0.1-5 m²/g.

Average diameters of aggregated particles greater than said range or anyBET specific surface area smaller than said range are not preferablebecause high temperatures are required for preparation thereof, and acomparable increase in performance is hardly obtained for use as anactive material for batteries. Further, average diameters of aggregatedparticles smaller than said range or BET specific surfaces area greaterthan said range are also not preferable, because packing deteriorates inuse as an active material for batteries and Mn dissolution from thestructure along with other problems which readily occur.

Preferably, the spinel-type lithium-manganese oxide containing at leastone heteroelement according to the present invention has a primaryparticle diameter of less than 3 μm. Values greater than said range arenot preferable because no higher performance is hardly realized for useas an active material for batteries. In the spinel-typelithium-manganese oxide containing at least one heteroelement accordingto the present invention, the symbol (y) representing the content of theheteroelements is in the range of 0<y≦1.0. When two or moreheteroelements are contained, the contents of various heteroelements arerepresented by y1, y2, y3, . . . yn, and satisfy 0<y1+y2+y3+ . . . +yn≦1.0.

Total amounts of said (ys) of 1.0 or more are not preferable becausecharge/discharge capacity becomes lower.

In the spinel-type lithium-manganese oxide containing at least oneheteroelement according to the present invention, Li exists at both ofthe oxygen tetrahedral sites and oxygen octahedral sites in the spinelstructure so that the proportion (x) of the content existing at theoxygen octahedral sites to the content existing at the oxygentetrahedral sites satisfies 0<x≦0.33.

Total amounts of Li of less than 1 are not preferable because amono-phase spinel structure can not be obtained, or Mn dissolution intothe organic electrolyte increases. Further, total amounts greater thansaid range are also not preferable, because charge/discharge capacitybecomes lower.

The value of said (x) within a range of 0≦x≦0.15 is especiallypreferable, because a high capacity can be achieved and Mn dissolutioncan be kept low.

When one heteroelement other than Li and Mn is contained in the oxideaccording to the present invention, the element is preferably Cr.

When the heteroelement is Cr, the formula of the compound according tothe present invention is represented as follows:

{Li}[Li_(x).Mn_((2−x−y)).Cr_(y)]O_(4+d)

wherein { } represents the oxygen tetrahedral sites in the spinelstructure and [ ] represents the oxygen octahedral sites in the spinelstructure, with 0<x≦0.33, 0<y≦1.0, −0.5<d<0.8.

In this case, it is preferred that 0<x≦0.15 and 0. 02≦y≦0.2.

When two heteroelements (M(1), M(2)) other than Li and Mn are containedin the oxide according to the present invention, the formula of thecompound according to the present invention is represented as follows:

{Li}[Li_(x).Mn_(2−x−y1−y2).M(1)_(y1).M(2)_(y2)]O_(4+d)

wherein { } represents the oxygen tetrahedral sites in the spinelstructure and [ ] represents the oxygen octahedral sites in the spinelstructure, 0<x≦0.33, 0<y1+y2≦1.0, −0.5<d<0.8, and M(1) and M(2)represent elements other than Li and Mn.

Preferably, one of the heteroelements M(1) contained is Cr and the otherM(2) is a transition metal.

More preferably, one of the heteroelements M(1) contained is Cr and theother M(2) is Fe, as represented by the following formula:

{Li}[Li_(x).Cr_(y1).Fe_(y2).Mn_(2−x−y1−y2)]O_(4+d)

wherein { } represents the oxygen tetrahedral sites in the spinelstructure and [ ] represents the oxygen octahedral sites in the spinelstructure, with 0<x≦0.33, 0<y1≦0.5, 0<y2≦0.5, −0.5<d<0.8.

In the above formula, it is preferred that 0<x≦0.15, 0<y1≦0.2 and0<y2≦0.2.

The spinel-type lithium-manganese oxide containing at least oneheteroelement according to the present invention contains Li at theoxygen tetrahedral sites as well as Li, Mn and at least oneheteroelement (M) other than Li and Mn at the oxygen octahedral sites inits spinel structure, and it has a particle structure providing highperformances when it is used as an active material for a battery.

The spinel-type lithium-manganese oxide containing at least oneheteroelement according to the present invention can be prepared bymixing and calcining a manganese compound, a lithium compound and eachcompound of a heteroelement to be contained.

Compounds capable of producing an oxide at or below the calcinationtemperature selected from oxides, hydroxides, hydroxide oxides,carbonates, chlorides, nitrates, sulfates, etc. can be mixed, butoxides, hydroxides, hydroxide oxides and carbonates are especiallypreferable in respect of reactivity and environmental influences ofwaste gases.

It is essential to use a manganese oxide having an average diameter ofaggregated particles of 0.5-50 μm as a starting manganese compound, andthe starting manganese compound preferably has a molding density of notless than 2.7 g/cm³.

It is not preferable to use any manganese oxide outside said range,because a product satisfying particle characteristics of the spinel-typelithium-manganese oxide containing at least one heteroelement accordingto the present invention can hardly be obtained from such a manganeseoxide.

It is also preferable to use a starting manganese compound having Na andK contents of not more than 500 ppm. It is difficult to prepare ahigh-performance Li secondary battery when a product with a startingcompound having higher Na and K contents is used as an active materialfor the battery.

In the process for preparing a spinel-type lithium-manganese oxidecontaining at-least one heteroelement according to the presentinvention, it is preferable to use a lithium compound having a BETspecific surface area of not less than 1 m²/g as the starting lithiumcompound.

Examples of the lithium compound include carbonates, nitrates,chlorides, hydroxides, oxides, etc., among which it is very preferableto use lithium carbonate having a BET specific surface area of not lessthan 1 m²/g because a homogeneous spinel-type lithium-manganese oxidecontaining at least one heteroelement can be readily prepared even inthe air.

In the process for preparing the spinel-type lithium-manganese oxidecontaining at least one heteroelement according to the presentinvention, the calcination temperature is appropriately selected toobtain desired particle characteristics within a range of 500 to 1000°C.

Calcination temperatures outside said range are not preferable becausethe BET specific surface area and/or primary particle diameter of theresulting product does not fall within a desired range.

Calcination may be conducted either in air or an oxygen-rich atmosphere.However, it is preferably conducted in air for the sake of simplicity ofthe structure of the calcination furnace.

Under the preparation conditions described above, it is especiallypreferable to adopt the following procedures.

1. Mixing a manganese compound, a lithium compound and each compound ofa heteroelement, thereafter granulating and then calcining the mixture.

2. Mixing a manganese compound and a lithium compound, granulating andcalcining the mixture, thereafter formulating a lithium compound and/oreach compound of a heteroelement to be contained, then granulating andthen calcining the mixture.

3. Mixing a manganese compound, a lithium compound and each compound ofa heteroelement to be contained, granulating and calcining the mixture,thereafter formulating any one of a manganese compound, a lithiumcompound and each compound of a heteroelement to be contained, thengranulating and then calcining the mixture.

Any conventional means can be used so far as materials can behomogeneously mixed thereby. Calcination may also preferably beconducted with mixing in a rotary kiln or the like.

The resulting spinel-type lithium-manganese oxide is preferably groundand classified at an appropriate moment.

According to the present invention, a Li secondary battery was preparedusing a spinel-type lithium-manganese oxide prepared as above as anactive material for positive electrode.

Suitable active materials for negative electrode to be used in thelithium secondary battery according to the present invention include ametallic lithium and a material capable of occluding and releasinglithium or lithium ions. Specific examples thereof include metalliclithium, lithium/aluminium alloys, lithium/tin alloys, lithium/leadalloys and carbonaceous materials electrochemicallyintercalated/deintercalated with lithium ions. Among them, carbonaceousmaterials electrochemically intercalated/deintercalated with lithiumions are especially preferable in respect of safety and batterycharacteristics.

Suitable electrolytes to be used in the lithium secondary batteryaccording to the present invention include, but are not specificallylimited to, solution of a lithium salt dissolved in an organic solventsuch as carbonates, sulfolanes, lactones, ethers; or a solid electrolyteconductive of lithium ion.

A battery shown in FIG. 1 was constructed using the spinel-typelithium-manganese oxide according to the present invention as an activematerial for positive electrode.

The battery in FIG. 1 includes cathode collector 8, cathode 7, separator6, anode 5 anode collector 4 and cap 1 positioned sequentially on case 3and centered by gasket 2 within case 3.

According to the present invention, a stable lithium secondary batterywith high performances can be obtained by using the foregoing materialsas an active material for positive electrode, an active material fornegative electrode and a non-aqueous electrolyte containing a lithiumsalt.

The following examples illustrate the present invention, but are notconstrued to limit the same.

EXAMPLES

Various measurements in the following examples of the present inventionand comparative examples were made under the following conditions.

X-ray diffraction (XRD) patterns were determined under the followingconditions.

Instrument model: Material Analysis and Characterization Corp. Ltd.,MXP-3

Irradiation X-rays: Cu Kα rays

Measurement mode: step scanning

Scanning condition: 0.04°/sec.

Measurement period: 3 seconds

Measurement range: 2θ ranging from 5°-80°.

Elemental analyses were performed by ICP spectrometry.

The oxidation degree of the elemental Mn was determined by an oxalatemethod.

SYNTHESIS OF SPINEL-TYPE LITHIUM-MANGANESE OXIDES

Examples and comparative examples of spinel-type lithium-manganeseoxides were synthesized in the following manner.

Examples 1-5

Cr was used as the heteroelement M. The composition of the followingformula:

{Li}[Li_(0.06).Cry.Mn_((2−0.06−y))]O₄

was prepared by weighing MnO₂ having an average diameter of aggregatedparticles of 20 μm (electrolytic manganese dioxide made by TOSOH CORP.),lithium carbonate (Li₂CO₃) having a BET specific surface area of 3 m²/gand chromium oxide (Cr₂O₃) having an average diameter of aggregatedparticles of 1 μm with a varying ratio between Cr and Mn while the Licontent expressed as (x) being fixed at 0.06 (Li:(Mn+Cr)=1.10:2.00) inthe above formula, thoroughly mixing these components in a mortar,thereafter calcining the mixture provisionally at 450° C. for 24 hours,then at 750° C. for 24 hours.

The particle structure of the spinel-type lithium-manganese oxideobtained in Example 3 was observed by SEM. The SEM 20,000 magnificationmicrophotograph thereof is shown in FIG. 2.

It was found from the figure that all particles of the spinel-typelithium-manganese oxide have a primary particle diameter of not morethan 1 μm, and an average primary particle diameter of not more than 1μm.

Further, it was estimated from the lattice constant value from X-raydiffraction and the Rietveld Analysis that the obtained spinel-typelithium-manganese oxides have the chemical formula as stated above.

Example 6

The procedure of Example 3 was repeated except that the finalcalcination temperature was increased from 750° C. to 900° C.

The particle structure of the obtained spinel-type lithium-manganeseoxide was observed by SEM. The SEM 20,000 magnification microphotographthereof is shown in FIG. 3.

It was found from the figure that spinel-type lithium-manganese oxideincludes some particles having a primary particle diameter of not lessthan 1 μm, but has an average primary particle diameter of not more than3 μm.

Example 7

The procedure of Example 4 were repeated except that the Li content waschosen at a value of (x) of 0.02.

Examples 8-10

The procedure of Examples 2-4 was repeated except that Cr was replacedby Co. Basic cobalt carbonate was used as a starting Co material.

Examples 11-13

The procedure of Examples 2-4 was repeated except that Cr was replacedby Ni. Basic nickel carbonate was used as a starting Ni material.

Examples 14-16

The procedure of Examples 2-4 was repeated except that Cr was replacedby Fe. Fe₃O₄ was used as a starting Fe material.

Example 17

Using Cr as a first heteroelement M1 and Fe as a second heteroelementM2, the composition of the following formula:

{Li}[Li_(0.01).Cr_(0.1).Fe_(0.1).Mn_(1.79)]O₄

was prepared by weighing MnO₂ having an average diameter of aggregatedparticles of 20 μm, Li₂CO₃ having a BET specific surface area of 3 m²/gas well as Cr₂O₃ and Fe₃O₄ both having an average diameter of aggregatedparticles of 1 μm so that the Li content expressed as (x) is 0.01(Li:(Li+Mn+Cr+Fe)=1.01:3.00) with (y1) being 0.1 and (y2) being 0.1 inthe above formula, thoroughly mixing these components in a mortar,thereafter calcining the mixture provisionally at 450° C. for 24 hours,then at 750° C. for 24 hours.

Comparative Example 1

MnO₂ having an average diameter of aggregated particles of 20 μm(electrolytic manganese dioxide made by TOSOH CORP.) and lithiumcarbonate having a BET specific surface area of 3 m²/g were weighed sothat x=0.0 (Li:Mn=1.00:2.0) and thoroughly mixed in a mortar, thereaftercalcined provisionally at 450° C. for 24 hours, then at 750° C. for 24hours.

The product showed a similar pattern to that of LiMn₂O₄ of a JCPDS card35-782.

Comparative Example 2

The procedure of Comparative example 1 was repeated except that x=0.10(Li:Mn=1.10:2.0).

Comparative Example 3

The procedure of Comparative example 1 was repeated except that x=0.15(Li:Mn=1.15:2.0).

Comparative Example 4

The procedure of Comparative example 1 was repeated atLi:Cr:Mn=0.95:0.2:1.80 and calcined under the conditions of Comparativeexample 1.

The products of the examples and comparative examples showed a cubicspinel structure in single phase except for that of Comparative example4.

Mn DISSOLUTION TEST

Each 3 g of the lithium-manganese oxides prepared in the examples andcomparative examples was placed in 15 ml of an electrolyte of lithiumhexafluoride phosphate dissolved in a mixed solvent of ethylenecarbonate and dimethyl carbonate at a concentration of 1 mole/dm³, andmaintained at 85° C. for 100 hours, after which the Mn content in theelectrolyte was analyzed by ICP spectrometry.

The results are shown in Table 1.

CONSTRUCTION OF BATTERIES

Samples of the lithium-manganese oxides obtained in the examples andcomparative examples before and after the above Mn dissolution test wereused in a battery test. For the battery test, each sample was mixed witha conductive mixture of polytetrafluoroethylene and acetylene black(trade name: TAB-2) at a weight ratio of 2:1. The mixture was pelletizedon a mesh (SUS 316) under the pressure of 1 ton/cm², and then dried invacuo at 200° C. for 24 hours.

A battery as shown in FIG. 1 was constructed by using the thus obtainedpellet as a positive electrode 3 in FIG. 1, a lithium piece cut out froma lithium foil (0.2 mm in thickness) as a negative electrode 5 in FIG.1, a solution of lithium hexafluoride phosphate dissolved in a mixedsolvent of propylene carbonate and diethyl carbonate at a concentrationof 1 mole/dm³ as an electrolyte with which a separator 4 in FIG. 1 isimpregnated, and a carbonaceous material electrochemicallyintercalated/deintercalated with lithium ions as an active material fornegative electrode.

EVALUATION OF BATTERY CHARACTERISTICS

Batteries were prepared by using the lithium-manganese oxides preparedin the examples and comparative examples as an active material forpositive electrode, and repeatedly cycled between charge and dischargeat a constant current of 1.0 mA/cm² and a battery voltage from 4.5 V to3.5 V.

The test was run at room temperature and at 50° C.

Table 1 shows initial capacities, capacity retention (% of dischargecapacity at the 50th cycle to 10th cycle) and dissolution test retention(% of the capacity after dissolution test to initial capacity beforedissolution test).

ADVANTAGES OF THE INVENTION

The spinel-type lithium-manganese oxide of the present invention showsless dissolution of Mn in an organic solvent, stable charge/dischargecycling characteristics even after long-term storage and lessdeterioration during charge/discharge at high temperatures.

Capacity Dissolution Hetero- Mn Lattice Initial retention test Licontent element Dissolution constant BET capacity (%) retention (1 + x)M y (mol %) (A) (m²/g) (mAH/g) RT, 50° C. (%) Ex.1 1.06 Cr 0.01 0.658.237 1.75 120 — — — Ex.2 1.06 Cr 0.02 0.49 8.235 1.58 120 — — — Ex.31.06 Cr 0.1 0.09 8.230 2.31 108 99 94 90 Ex.4 1.06 Cr 0.2 0.11 8.2231.83 94 99 95 95 Ex.5 1.06 Cr 0.4 0.14 8.209 1.80 63 97 95 95 Ex.6 1.06Cr 0.1 0.07 8.237 0.90 103 99 94 90 Ex.7 1.02 Cr 0.2 0.20 8.242 2.11 11595 90 85 Ex.8 1.06 Co 0.02 0.64 8.231 1.41 120 — — — Ex.9 1.06 Co 0.10.52 8.228 1.60 108 96 91 81 Ex.10 1.06 Co 0.2 0.49 8.196 1.43 93 96 9285 Ex.11 1.06 Ni 0.02 0.62 8.234 1.56 117 — — — Ex.12 1.06 Ni 0.1 0.238.219 1.73 93 95 92 88 Ex.13 1.06 Ni 0.2 0.13 8.202 1.66 63 96 92 90Ex.14 1.06 Fe 0.02 0.49 8.235 1.68 120 90 88 81 Ex.15 1.06 Fe 0.1 0.318.237 2.11 108 92 90 85 Ex.16 1.06 Fe 0.2 0.18 8.234 2.12 93 99 95 96Ex.17 1.01 Cr 0.1 0.05 8.239 1.88 107 99 95 94 Fe 0.1 Com.1 1.00 — 0.01.06 8.242 1.80 130 90 60 60 Comp.2 1.10 — 0.0 0.84 8.234 1.75 123 94 8375 Comp.3 1.15 — 0.0 0.83 8.219 1.62 106 95 84 76 Comp.4 0.95 Cr 0.20.95 — 1.70 — — — —

What is claimed is:
 1. A spinel-type lithium-manganese oxide representedby the following formula:{Li}[Li_(x).Mn_(2−x−y1−y2).M1_(y1).M2_(y2)]O_(4+d), wherein { }represents oxygen tetrahedral sites in a spinel structure, [ ]represents oxygen octahedral sites in the spinel structure, 0<x≦0.33,0<y1+y2≦1.0, −0.5<d<0.8, M1 and M2 are each at least one transitionmetal other than Mn, and M1 and M2 are different.
 2. The spinel-typelithium-manganese oxide according to claim 1, which has a cubic crystalstructure having a lattice constant a of not less than 8.19 angstromsand not more than 8.24 angstroms.
 3. The spinel-type lithium-manganeseoxide according to claim 1, which has an average primary particlediameter of not more than 3 μm.
 4. The spinel-type lithium-manganeseoxide according to claim 1, which has an average diameter of aggregatedparticles of 1-50 μm and a BET specific surface area of 0.1-5 m²/g. 5.The spinel-type lithium-manganese oxide according to claim 1, wherein M1is Cr.
 6. The spinel-type lithium-manganese oxide according to claim 5,wherein 0<x≦0.15 and 0.02≦y1+y2≦0.2.
 7. A method of using a spinel-typelithium-manganese oxide, the method comprising using the spinel-typelithium-manganese oxide of claim 1 in an electrode of a Li secondarybattery.
 8. A Li secondary battery comprising a positive electrode, anegative electrode, a non-aqueous electrolyte that comprises aLi-containing electrolyte dissolved therein, and a separator, whereinthe spinel-type lithium-manganese oxide of claim 1 is used as an activematerial for the positive electrode.
 9. The Li secondary batteryaccording to claim 8, wherein a carbonaceous material electrochemicallyintercalated/deintercalated with lithium ions is used as an activematerial for the negative electrode.
 10. A process for preparing aspinel-type lithium-manganese oxide, the process comprising mixing andcalcining a starting manganese compound, a starting lithium compound andat least two transition metals; and forming the spinel-typelithium-manganese oxide of claim 1, wherein a manganese oxide having anaverage diameter of aggregated particles of 0.5-50 μm is used as thestarting manganese compound.
 11. The process according to claim 10,wherein a density of the starting manganese compound is not less than2.7 g/cm³.
 12. The process according to claim 10, wherein Na and Kcontents in the starting manganese compound are each not more than 500ppm.
 13. The process according to claim 10, wherein BET specific surfacearea of the starting lithium compound is not less than 1 m²/g.
 14. Theprocess according to claim 13, wherein lithium carbonate is used as thestarting lithium compound.
 15. The process according to claim 10,wherein the calcining is conducted at a temperature of 500 to 1000° C.in air.
 16. The process according to claim 10, further comprisinggranulating the starting manganese compound, the starting lithiumcompound and the at least two transition metals to form a mixture beforecalcining the mixture.
 17. A spinel-type lithium-manganese oxiderepresented by the following formula:{Li}[Li_(x).Mn_(2−x−y1−y2).M1_(y1).M2_(y2)]O_(4+d), wherein { }represents oxygen tetrahedral sites in a spinel structure, [ ]represents oxygen octahedral sites in the spinel structure, 0<x≦0.33,0<y1+y2≦1.0, −0.5<d<0.8, M1 and M2 are each at least one transitionmetal other than Mn, and M1 and M2 are different, wherein M1 is at leastCr and M2 is Fe at least.
 18. The spinel-type lithium-manganese oxideaccording to claim 17, wherein 0<x≦0.15, 0<y1≦0.2 and 0<y2≦0.2.
 19. Amethod of using a spinel-type lithium-manganese oxide, the methodcomprising using the spinel-type lithium-manganese oxide of claim 17 inan electrode of a Li secondary battery.